Pressing tools are used to compress coupling elements and thus join two parts together. Cylindrical coupling elements include, for example, pressed sleeves, pressed fittings or pipe joints, and also pipe segments which can be inserted into one another and pressed together. Pressing tools can have a pistol shape and a clamping claw. The clamping claw encloses a coupling element to be compressed. When the pressing tool is activated, the clamping claw is pressed together, which in turn compresses the coupling element. In order to permit the same pressing tool to be used with coupling elements of different diameters, the tool is configured such that clamping claws with corresponding dimensions can be easily substituted. Therefore, the pressing tool can include a forked receiver, in which the clamping claw is interchangeably attached by a connecting pin. The forked receiver and the clamping claw have bored holes for this purpose, through which the connecting pin is inserted.
Pressing tools of this type are prone to cause accidents. For example, the clamping claw has been known to fly off uncontrollably and the forked receiver is forced apart and bent. Mishaps or accidents have occurred with both electro-mechanical pressing tools as well as electro-hydraulic pressing tools. While the exact cause of these accidents is not known, it is assumed that material fatigue, manufacturing tolerances and power fluctuations were significant factors in the accidents.
An additional potential cause of the above-mentioned accidents is that the connecting pin may have been incorrectly or incompletely inserted into the forked receiver. In that case, the transverse forces that occur during the pressing operation cause the forked receiver to be spread apart, thereby allowing the clamping claw to become detached from its mounting. It is therefore important that the correct position of the connecting pin be monitored, and that the drive motor of the pressing tool be disabled should the monitor detect that the connecting pin is not completely seated within its bore.
There are other pressing tools for cylindrical coupling elements in which the connecting pin is secured by a safety element, such as a split pin. The split pin only serves to secure the connecting pin in position, and not to monitor the position of the pin within its bore. The pressing tool is also capable of operation without this safety device, so there is no real increase in operating safety. Because this type of work is usually done under time pressure, with the claws having to be changed frequently, the split pins are often not employed.